Thin-film microelectromechanical device fabrication process

ABSTRACT

Processing and systems to create, and resulting products related to, very small-dimension singular, or monolithically arrayed, semiconductor mechanical devices. Processing is laser performed on selected semiconductor material whose internal crystalline structure becomes appropriately changed to establish the desired mechanical properties for a created device.

RELATED APPLICATIONS

This application is a continuation of a pending patent application entitled, SEMICONDUCTOR CRYSTAL-STRUCTURE-PROCESSED MECHANICAL DEVICES AND METHODS AND SYSTEMS FOR MAKING, invented by John Hartzell, Ser. No. 10/131,057, filed Apr. 23, 2002. This application is incorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention arises from a new area of recognition and development focussed on the technology of low-temperature, crystalline-structure-processed devices, and in particular mechanical, mechanical and electrical, so-called MEMS (micro-electromechanical), layered and stacked devices, and devices organized into monolithic arrays in layers, that opens up a broad new field of potential devices and applications not heretofore so inexpensively and conveniently made practical and practicable. This new field of possible devices, from which a number of inventions, one of which is specifically addressed in this disclosure, springs effectively from the recognition that internal crystalline-structure processing performed within the bodies of a wide variety of different materials, is capable of enabling fabrication of small (perhaps even down to devices formed from small molecular clusters), versatile, widely controllable and producible, accurate, mechanical, electromechanical and MEMS devices that can be formed very inexpensively, and, with respect to laser processing, in uncontrolled and room-temperature environments not requiring vacuum chambers, etc.

Especially, the invention offers significant opportunities for the building, relatively cheaply and very reliable, of very tiny semiconductor mechanical devices that can be deployed in dense two-dimensional and three-dimensional complex arrays and stacked arrangements. These devices can take on a large range of different configurations, such as individuated, single-device configurations, monolithic single-layer array arrangements of like devices, similar monolithic arrays of combined electrical and mechanical devices, and in vertically integrated and assembled stacks and layers of complex devices, simply not achievable through conventional prior art processes and techniques. By enabling room-temperature fabrication, otherwise easily damaged and destroyed layer-supporting substrates, including fabricated-device under-layers, can readily be employed.

The field of discovery and recognition which underpins the invention disclosed herein, can be practiced with a very wide range of semiconductor materials in arrays that can be deployed on rigid substrates of various characters, and on a wide range of flexible materials, such as traditional flex-circuit materials (polymers and plastics), metallic foil materials, and even fabric materials. Additionally, the field of development from which the present invention emerges can be employed with large-dimension bulk materials, as well as with various thin-film materials. The present invention is described in this broader-ranging setting. With regard to the latter category of materials, the process of this invention can take advantage of traditional thin-film semiconductor processing techniques to shape and organize unique devices, which are otherwise prepared in accordance with the internal crystalline-structure-processing proposed by the present invention, thus to achieve and offer mechanical properties in a broad arena of new opportunities.

In this setting, the invention disclosed in this document is specifically related to crystal-structure-processed semiconductor mechanical devices, either as individuated, single devices, or in arrays of devices organized into monolithic, layer-type arrangements, as well as to methodology and system organizations especially suited to the preparation and fabrication of such devices. The invention proposed a unique way, employing, for example, different types of lasers and other illumination sources. effectively to “reach into” the internal crystalline structures different semiconductor materials for the purpose of controllably modifying those structure to produce advantageous mechanical properties in devices, and at sizes very difficult and sometimes not even possible to create via prior art techniques.

From the drawings and the descriptions which now follow, it will become readily apparent how the present invention lends itself to the economic, versatile, multi-material fabrication and use of a large variety of devices, ranging from relatively large devices to extremely small device as mentioned earlier), and including various forms of MEMS devices, without the fabrication of these devices, insofar as laser processing involved, necessitating the use of special controlled processing environments, or surrounding processing temperatures above typical room temperature.

With this in mind, the significant improvements and special contributions made to the art of device-fabrication according to the invention will become more fully apparent as the invention description which now follows is read in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block/schematic view illustrating a system which implements the methodology of this invention for the creation of single or arrayed semiconductor mechanical devices in accordance with the present invention.

FIG. 2 is a schematic diagram illustrating single-side, full-depth internal-crystalline-structure laser processing to create a semiconductor mechanical device in accordance with the invention.

FIG. 3 is very similar to FIG. 2, except that here what is shown is two-sided processing according to the invention.

FIG. 4 is a view similar to FIG. 2, but here showing processing occurring from an opposite side of material in accordance with the invention.

FIG. 5 is a view illustrating single-side, partial-depth internal-crystalline-structure processing according to the invention.

FIG. 6 is similar to FIG. 2, except that here single-side processing includes a flood, or wash, of general heating illumination according to one form of practicing the invention, with this illumination striking material on what is shown as the upper side in FIG. 6.

FIG. 7 is similar to FIG. 6, except that it illustrates two-sided processing wherein a relatively translated laser beam processes the upper side of material as pictured in FIG. 7, and a wash, or flood, of other illumination (from a laser or another light soruce) aids from the bottom side of material as pictured in FIG. 7. FIG. 7, in particular, illustrates a condition where material that is being processed in accordance with the invention is resting on a substrate which is not transparent to the wash of illumination coming from the bottom side of FIG. 7.

FIG. 8 is similar to FIG. 7, except that here the material being processed is resting on a substrate, such as glass, which is essentially transparent to a wash of illumination striking from the bottom side of FIG. 8.

FIGS. 9 and 10 illustrate two different views of a stylized micro-cantilever beam structure (mechanical device) constructed in accordance with the invention.

FIG. 11 shows an isolated view of a single micro-cantilever mechanical beam structure with a darkened region presented in this figure to illustrate, variously, sensitizing of a surface of the beam for the detection of a mechanical event, a chemical event, a biological event, etc. and also generally suggesting how, nested within the mechanical material making up the cantilever beam of FIG. 11 an electronic structure, such as a transistor, could be formed in a portion of the cantilever beam.

FIG. 12 is a view illustrating single-side, full-depth internal crystalline-structure processing of bulk material in accordance with the present invention.

FIG. 13 is similar to FIG. 12, except that here what is shown is single-side, partial depth, bulk-material processing. FIGS. 12 and 13 are included to give a broad understanding of the underlying overall field in which the present invention finds its place.

FIG. 14 is a view illustrating internal-crystalline-structure processing employing a single-crystal seed which is employed to characterize the end-result internal crystalline structure that can be achieved in the material pictured in FIG. 14.

FIG. 15 is a stylized, schematic, isometric view illustrating fragmentarily a single planer array of plural mechanical devices prepared in a single monolithic, generally planar structure in accordance with the present invention.

In FIGS. 2, 3, 4, 5, 6, 7, 8, 12 and 13, the darkened regions in the material being processed represents the processed regions in these materials.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, and referring first of all to FIG. 1, illustrated generally at 20 is a system which is employed according to the present invention to implement a methodology for processing the internal crystalline structure of various different semiconductor materials in accordance with the invention, and all for the purpose of creating one or more mechanical devices that are intended to perform respective, predetermined, pre-chosen tasks. Included in system 20 are a block 22 which represents a suitably programmed digital computer, a block 24 which is operatively connected to block 22, and which represents the presence of appropriate laser structure and controls, such as beam-shaping and optics controls using optical or masking methods, fluency controls, angularity controls, and other, for defining the functional characteristics of a appropriate laser beam shown at 26 which is to be employed in accordance with the invention to produce internal crystalline-structure processing of any one of a number of different semiconductor materials, as will be more fully mentioned below. In FIG. 1, a material for processing is shown generally at 28, with this material having a layer form, and being suitably supported on an appropriate supporting substrate 30 which rests upon, and is anchored to, a three-axis translation table (a driven table) 32.

Table 32 is drivingly connected to a motion drive system, represented by block 34 in FIG. 1, which drive system is under the control of computer 22. This motion drive system, under the control and influence of computer 22, is capable of translating table 32, and thus material supported on this table, in each of the three usual orthogonal axes known as the X, Y, and Z axes, such axes being pictured at the right side of FIG. 1. Very specifically, control over motion of table 32 is directed by an appropriate algorithm 36 which is resident within computer 22, and which, fundamentally, is equipped to direct a laser beam for processing in accordance with device configuration and device internal mechanical properties that have been chosen and selected, and for which algorithm 36 is especially designed.

The exact nature of the construction of computer 22, of controls 24, of algorithm 36, and of the driven table and the motion drive therefor, form no part of the present invention, and accordingly are not further detailed herein.

Fundamentally, what takes place in the operation of system 20 to produce a given type of mechanical device is that a user selects a particular kind of device to build, selects an appropriate size and configuration for that device, and then determines what are the best and most appropriate internal mechanical properties that should be created in that device in order to enable it to function properly with respect to implementing a selected task. In general terms, the semiconductor materials out of which a particular material can be selected to produce such a device are those whose internal crystalline structures are closely linked to the material's mechanical properties. Specifically, the various useable semiconductor materials are those whose internal crystalline structures can be modified by laser processing to produce desired mechanical properties for a device. Various materials with respect to which the present invention can conveniently and very successfully work will be discussed very shortly, but it might be noted at this point that these materials, with respect to their precursor states, i.e. their states before processing, range from fully amorphous materials through and into a range of various categories of polycrystalline materials.

For example, practice of the invention can begin with precursor material which can fit into any one of the following categories: amorphous, nanocrystalline, micro-crystalline, and polycrystalline. All such materials can be generally described as having an internal crystalline structure which, initially in a precursor state, is less than single crystalline in nature.

Semiconductor materials which can very successfully be processed in accordance with this invention include silicon, germanium and silicon-germanium. For the purpose of further illustration in this description, a manner of practicing the invention, and a device emerging from that practice, will be described in conjunction with full-layer-depth processing of a precursor amorphous silicon material, which will thus be treated as the specific kind of material which is pictured at 28 in FIG. 1. Also for the purpose of focused illustration herein, this precursor illustrative amorphous silicon material is deployed as an appropriate thin layer on a glass substrate, which is designated by reference numbered 30 in FIG. 1. Other substrate materials, as will become apparent, may include quartz, various metals, plastics, flex materials, fabrics and others. All of these materials have what are referred herein as relatively low melting (or destruction) temperatures which are well below the melting temperature of the silicon precursor material.

As has already been suggested above, practice of the present invention can produce a wide variety of uniquely configured and constructed semiconductor mechanical devices which can be extremely small in size, ranging down even to a small molecular cluster size. Devices which can be produced include various MEMS devices, micro-mechanical devices that are sensitized to act as sensors for various environmental events, such as chemical and biological events, various motion elements generally, oscillating elements, cantilever beams, actuators, relay switches, and other devices.

With respect to formation of a particular device's three-dimensional configuration, this can be done in any one of a number of conventionally known ways. The exact processes employed to give three-dimensional definition to a finally produced device, as for example to singulate an element from a mass of material in which it has been formed, and/or to individuate (for performance purposes) plural devices in a monolithic array of devices, can take the form of various conventional processes which form no particular parts of the present invention. Thus they are not discussed herein in detail.

For the purpose of illustration herein, processing will be described in the setting, initially, of creating a single micro-mechanical cantilever mechanical device, using single-side, translated laser-beam processing. While various specific types of lasers can be employed such as a excimer laser, a solid-state laser, a continuous-wave laser, and a femto laser, to name several, description will proceed in the context of using an excimer laser.

Describing now a typical practice implemented by the present invention, an amorphous silicon layer having an appropriate precursor thickness is suitably formed on the surface in a glass substrate, such as substrate 30. This assembly is placed on table 32 with appropriate initial alignment, and is then translated relatively with respect to a laser beam, such as excimer laser beam 26, which beam is pulsed during translation of the material relative to the source of the laser beam, to produce full-depth, small-area quick melting and re-crystallizing of the silicon material. An appropriate excimer laser, driven and pulsed at an appropriate pulse rate, and with an appropriate fluency and footprint in the sense of how and with what outlines it strikes the surface of the amorphous silicon material, is directed toward this surface under the control of computer 22, algorithm 36, and controls 24.

In accordance with the desired end-result internal crystalline structure, and in a relative motion sense, the impingement point of this beam from a laser is moved in a defined way over the surface of the amorphous silicon material to produce rapid, full-depth melting and re-crystallizing in a manner designed to achieve the pre-determined desired internal crystalline structure. Employing an excimer laser in this fashion allows one to process material in such a fashion that the high-temperature events are essentially confined very locally to the regions specifically where material melt is occurring. Very little, and no dangerous, temperature rise occurs in the surrounding area, such as within substrate 30, and the whole process can take place in a normal atmospheric environment and completely at room temperature.

FIGS. 2, 3 and 4 show several different approaches to implement such laser processing. In FIG. 2 the laser beam strikes the surface of the amorphous silicon material on the upper side which is spaced away from supporting substrate 30. Processed material is indicated (darkened) at 27. In FIG. 3 dual-sided processing takes place with two laser beams cooperating on opposite sides of the material, with the lower beam effectively processing the underside of the silicon material through the transparency afforded by glass substrate 30. Such dual-sided laser processing effectively allows melting and re-crystallizing to take place simultaneously on opposite sides of the supported silicon material, and with each laser, therefore, requiring only a portion of the power required for similar processing to take place under the influence of a single laser beam. Where a mask is employed for beam shaping, this dual-laser approach promotes longer-term durability of such a mask—a typically expensive device, and which is subject to significant degradation at high laser power levels Two-sided dual-beam processing can also be effective to allow processing to be performed in otherwise difficult to reach areas with just a single processing beam.

In FIG. 4 single-side processing is demonstrated where, in this case, the processing laser beam is directed toward the silicon material from the bottom side (i.e. the substrate supported side) of this material.

FIG. 5 illustrates single-side, less than full-depth processing of the silicon material, here employed to create ultimately a mechanical device which effectively becomes a device that is composited with unprocessed material lying beneath it, as illustrated in FIG. 5.

FIGS. 6, 7 and 8 show different manners of modifying the kinds of laser processing illustrated in FIGS. 2-4 inclusive, and specifically a modified processing approach which employs an additional broad area wash of illumination 38 from another illumination source which could be, but is not necessarily, a laser source. In FIG. 6 this wash of illumination strikes the upper side of the silicon material in companionship with laser beam 26, and is effective essentially to create an overall temperature rise in the silicon material which permits a lower energy laser beam to perform appropriate full-depth processing. In FIGS. 7 and 8 this wash 38 of illumination is directed toward the underside of the silicon material and the supporting substrate, with FIG. 7 illustrating a condition where the substrate support material shown at 40 is not transparent to illumination. In this implementation of the invention, the silicon material which is being processed is heated in a conduction manner through heating of substrate 40. In FIG. 8, glass substrate 30 is again pictured, and here, the wash 38 of illumination passes through this substrate to heat the silicon material above the substrate directly.

According to practice of the invention, once a particular semiconductor mechanical device to build has been decided upon, the desired three dimensional configuration of this device is chosen, and algorithm 36 is designed to direct laser processing in such a fashion as to create a regional volume of material within the processed material on the substrate adequate for the ultimate individuation and singulation, if that is what is desired, of an end-result mechanical device. With such a chosen device configuration in mind, the most desired internal mechanical properties are predetermined, and algorithm 36 is also constructed so that it will control the operation of a laser beam, such as beam 26, to produce internal melting and re-crystallization in order to achieve an internal crystalline structure that will yield the desired mechanical properties. In some instances, it may be more appropriate to create differentiated regions of crystalline structure within a device being built in order to produce different specific mechanical properties in different within that material. Such is entirely possible utilizing the processing approach which has just been outlined above.

FIGS. 9 and 10 show a side cross section and an idealized top plan view of a stylized cantilever-beam mechanical device 42 which has been so defined by processing within the body of silicon material 28.

FIG. 11, in an idealized fashion, isolates an illustration of cantilever beam 42, and shows by way of suggestion, produced by the darkened patch which appears in FIG. 11, how an appropriate event sensor, such as a chemical sensor, a biological sensor, and other kinds of sensors could be applied, in any suitable manner, to the beam so as to respond to selected environmental events in a manner which causes deflection in the beam. The present invention is not concerned with the specific kinds of sensitivity for which a device, such as beam 42, is to be prepared, and thus details of how sensitizing can take place are not presented herein.

FIG. 11 can also be read to illustrate yet another interesting component offering of the present invention which is that it is possible to create within the mechanical body of the device, such as cantilever beam 42, an electronic device, such as a semiconductor transistor which can be thought of as being represented by the darkened patch appearing in FIG. 11.

FIGS. 12 and 13 illustrate use of the invention to modify internal crystalline structure inside a bulk material 43, either with a full-depth approach (FIG. 12) or with a partial-depth approach (FIG. 13) in accordance with the invention. These two figures are included here to help establish a part of the underlying background of this invention.

FIG. 14 illustrates still another processing approach which utilizes a single-crystalline material seed 44 which rests in a tiny indentation formed in an appropriate layer 45 of a supporting material, such as silicon dioxide. See 44 lies adjacent an amorphous layer 50 of silicon. Laser processing takes place with initial illumination of the seed, followed by the laser-beam progression from the seed in a defined pattern over the amorphous silicon material. This action causes the single crystalline character of the seed 44 to become telegraphed into the internal structure of silicon layer 50, thus to characterize the internal crystalline structure in this layer to make it more nearly single crystalline in structure at the conclusion of processing.

FIG. 15 illustrates, in simplified fragmentary form, a monolithic layer structure 52 of processed, initially amorphous material which as been processed in an array fashion, and at discrete locations, to create a monolithic array of mechanical devices such as the devices shown at 54. While it is certainly possible that each and every one of devices 54 is essentially the same in construction, and intended to perform the same kind of function, it is entirely possible, according to practice of the invention, to differentiate the functionalities and thus the structures of these arrayed elements.

It should thus be apparent that a unique process capable of creating a wide range of unique mechanical devices, down to small molecular cluster devices, with a high degree of precise control over internal mechanical properties, is made possible by the present invention. Also made possible is the opportunity to do this insofar as laser processing is involved, in a completely atmospheric environment and at room temperature, and also in a manner which is one that does not attack and destroy supporting structure, such as substrate structure.

Accordingly, while several embodiments and manners of practicing the invention, and a system for doing all of this, have been illustrated and described herein, it is appreciated that variations and modifications may be made without departing from the spirit of the invention. 

1-22. (canceled)
 23. A method for forming a microelectromechanical system (MEMS) thin-film device, the method comprising: providing a substrate; forming a precursor material overlying the substrate; laser annealing the precursor material; selectively crystallizing regions of the precursor material; in response to selectively crystallizing, modifying the mechanical properties of the regions; and forming a mechanical device with a mechanical body in the modified regions.
 24. The method of claim 23 further comprising: forming an electronic device within the mechanical body.
 25. The method of claim 24 wherein forming the electronic device within the mechanical body includes forming a transistor.
 26. The method of claim 23 wherein modifying the mechanical properties of the regions includes modifying mechanical properties in response to changing the regions from a first crystalline structure to a second crystalline structure.
 27. The method of claim 23 wherein forming the precursor material overlying the substrate includes forming a material selected from the group including silicon, germanium, silicon-germanium, dielectrics, copper, silicon dioxide, aluminum, tantalum, titanium, and piezoelectric materials.
 28. The method of claim 23 wherein providing the substrate includes providing a substrate material selected from the group including glass, quartz, plastic, metal, flex materials, fabrics, copper foil, metal foil, and low-melting temperature materials.
 29. The method of claim 23 wherein selectively crystallizing regions of the precursor material includes: directing an excimer laser beam at a surface of the precursor material; shaping the beam using a mask; and crystallizing a region of the precursor material using the shaped beam.
 30. The method of claim 23 wherein selectively crystallizing regions of the precursor material includes: crystallizing a surface region of the precursor material; and leaving material underlying the surface region unprocessed.
 31. The method of claim 23 wherein selectively crystallizing regions of the precursor material includes crystallizing internal regions of the precursor material.
 32. The method of claim 23 wherein forming the precursor material overlying the substrate includes depositing a thin-film.
 33. The method of claim 24 wherein forming the mechanical device with the mechanical body includes forming a mechanical body with a material having a first crystalline structure; and wherein forming the electronic device includes forming the electronic device from a material having a second crystalline structure.
 34. The method of claim 33 wherein the first crystalline structure is different from the second crystalline structure.
 35. The method of claim 33 wherein forming the mechanical body and the electronic device includes forming the mechanical body and electronic device from the same material, with the first crystalline structure being different than the second crystalline structure.
 36. The method of claim 23 wherein forming the mechanical device with the mechanical body in the modified regions includes forming a mechanical device selected from the group including a cantilever beam, an oscillating element, an actuator, and a relay switch.
 37. The method of claim 24 wherein forming the mechanical device with the mechanical body in the modified regions includes forming a cantilever beam; the method further comprising: sensitizing the cantilever beam to an environmental stimulus.
 38. The method of claim 37 further comprising: the cantilever beam reacting to an environmental stimulus; the electronic device responding to reactions in the cantilever beam.
 39. The method of claim 37 wherein the cantilever beam is sensitized to react to a stimulus selected from the group including lotion, chemical, and biological.
 40. A microelectromechanical system (MEMS) cantilever device comprising: a mechanical body made from a thin-film material; and an electronic device formed within the mechanical body.
 41. The device of claim 40 wherein the electronic device is a transistor. 